258 Analytical Notices of Books. 
Cygnus ferus, Meyer, and Cygnus Bewichii, Yarrell, are clearly made out, 
especially as regards the structure of the trachea and sternum in the new 
species, which is explained in two plates, the latter of which represents 
these parts in three stages of their progressivedevelopement. In the adult 
state of the new species, the trachea, of equal diameter throughout, 
enters the keel of the sternum, through which it passes to the end, 
where, inclining upwards and outwards, it passes into a cavity formed in 
the body of the bone by the separation of the bony plates, and produ- 
cing a convex protuberance on the inner surface of the sternum. In this 
cavity the trachea assumes a horizontal direction, and makes a considerable 
curve reaching within half an inch of the posterior edge of the sternum. 
It then returns to the keel, along the upper part of which it passes to the 
exterior edge of the bone, over which it is reflected to enter the body of 
the bird and become attached to the lungs. In a less perfect state of 
developement the trachea occupies one side only of the cavity in the 
body of the sternum; and at a still earlier period, it is found in the keel 
alone, not having yet passed into the horizontal portion of the bone, in 
which, however, the projection indicating the cavity is already strongly 
morked. 
In these particulars the new species differs materially from the Wild 
Swan, in which the trachea never assumes a horizontal direction, and does 
not even penetrate within the keel to the extent of one half of the length 
of the sternum. In the comparative length of the bronchi, and of the 
bone of divarication, in the form of the latter, in the uniform calibre 
of the tube of the trachea of the new species, and in other particulars, 
additional differences exist. These are clearly explained by Mr. Yarrell, 
who has also given comparative measurements of both species; and, in 
further illustration of his subject has indicated some differences in habit 
and in voice, the latter agreeing with the variation in the structure of the 
trachea. 
To the organs of voice in Birds Mr. Yarrell has for many years been 
especially attentive, and the result of his enquiries respecting them 
forms the subject of another communication in the present part. In this 
truly valuable paper Mr. Yarrell describes the organ as consisting of four 
parts: the glottis, or superior Jarynx; the tube of the trachea; the in- 
ferior larynx, with its muscles; and the bronchi. These parts are noticed 
